The present invention relates to a polycrystalline silicon wafer, and in particular relates to a silicon wafer having an outer diameter of 450 mm or more for use in mechanical testing.
The shape of a monocrystalline silicon wafer that is used in an LSI process is becoming a larger diameter with the times. This is because, if the wafer diameter can be enlarged, more semiconductor devices can be produced from a single wafer, and the unit price of chips can thereby be reduced.
Meanwhile, pursuant to the further miniaturization of devices, the quality requirements of silicon wafers are becoming even stricter. Thus, when the wafer size shifts to large products, it is necessary to resolve the issues of quality in addition to the issues of scaling, and there is a problem in that the market price of next-generation size monocrystalline wafers will be extremely expensive.
According to ITRS (International Technology Roadmap for Semiconductors), it is anticipated that the timing that the wafer size will shift from a diameter of 300 mm to a diameter of 450 will be around 2012, and the timing that the wafer size will shift from a diameter of 450 mm to a diameter of 675 mm will be around 2019, and it is considered that the pursuit of larger diameter and higher quality of wafers will continue into the future.
When the wafer size is changed, the case (FOSB) for transporting the wafers and the wafer case (FOUP) for moving the wafers between the respective processes will also change as a matter of course. Moreover, the shape of robots that transfer wafers and machines for manufacturing the devices also need to be newly designed and developed to match the next-generation size wafers.
Accordingly, when the wafer size shifts to large products, next-generation wafers will be used for performing various types of tests and verifications for various types of purposes. Among these tests and verifications, there are usages that do not necessarily require the use of an expensive monocrystalline silicon wafer.
For example, upon developing robots for transporting wafer cases or wafers, the intended testing can be performed without having to use a monocrystalline wafer so as long as the mechanical properties of the used wafer; for instance, the weight and strength of the wafer and gravitational sag of the wafer, are equivalent to those of a monocrystalline wafer.
Since this kind of wafer (hereinafter referred to as the “mechanical wafer”) is not a monocrystalline wafer that can actually be used for producing a device, it is extremely important that the mechanical wafer is of low cost. Accordingly, with a mechanical wafer, cost reduction must be sought while omitting unwanted quality, and it is necessary to understand the conditions so that the mechanical properties thereof will be the same level as those of a monocrystalline wafer.
By way of reference, to list past publications, as an LSI sintered silicon wafer, Patent Document 1 proposes a sintered compact having a crystal grain size of 100 μm or less, and Patent Document 2 proposes a sintered compact having an average grain size of 1 to 10 μm.
While these sintered silicon dummy wafers can increase the strength of the wafer by adjusting the transverse rupture strength, tensile strength, and Vicker's hardness, there is naturally a limit in causing the gravitational sag of these wafers to approach that of a monocrystalline silicon wafer, and this is the reason why the use of such sintered silicon dummy wafers as a mechanical wafer having a diameter of 450 mm or more is extremely limited.
Moreover, Patent Document 3 describes polycrystalline silicon having an outer diameter of 48 mm or more and 450 mm or less, and a method of reducing the roughness Ra and surface sagging. Nevertheless, the cause of cracks in polycrystalline silicon of 450 mm or more is not the roughness or sagging of the surface, but is rather caused by fine scratches. Thus, it cannot be said that Patent Document 3 has resolved the problems encountered in polycrystalline silicon of 450 mm or more.
When using polycrystalline silicon as a mechanical wafer, substantially the same behavior as monocrystalline silicon is expected, and it is extremely important that the polycrystalline silicon wafer does not deviate from both the bending strength and gravitational sag of a monocrystalline silicon wafer. With respect to this point, while it has been confirmed that the mechanical strength demanded in a mechanical wafer is considerably affected by the scratches on the polycrystalline silicon surface, no conventional technology has discovered a solution for resolving this problem.